136 W. W. SWINGLE 



It has been demonstrated by several investigators that abla- 

 tion of the pineal apparatus of amphibian embryos apparently has 

 little effect upon the growth and development of the pigmentary 

 system. It should be noted, however, that this gland when 

 extirpated in very young larvae has the power to regenerate, 

 hence it is possible that it may play a more important role in in- 

 ducing pigment changes than we think. It is certain that the 

 p neal gland exerts no such marked and continuous power over the 

 melanophore system as does the pars intermedia. 



It is interesting to note that the removal of the pars intermedia 

 causes persistent expansion of the xantholeucophores, and that 

 implantation brings about their contraction along with persist- 

 ent expansion of the melanophores. Here we are dealing with a 

 differential effect upon the pigmentary system of a single gland, 

 maximum expansion of the melanophores when an oversecretion 

 of pars intermedia is obtained, as, for instance, by transplan- 

 tation experiments, maximum expansion of the xantholeuco- 

 phores when the pars intermedia is lacking. Taking these facts 

 into consideration, it is possible that instead of dealing with differ- 

 ential effects of a single gland upon the tadpole's pigmentary ap- 

 paratus, we may be observing the effects of interaction between 

 two internal secretory mechanisms. It seems rather improbable 

 that the mere absence of the pars intermedia is capable of bring- 

 ing about maximum and continuous expansion of the xantholelco- 

 phores, such as occurs in 'pituitariless' frog larvae. It is improb- 

 able that the ' absence' of anything could act as a stimulus of the 

 strength required to produce this effect. Is it not possible that 

 the ablation of the pars intermedia has released some other active 

 agent within the body from an inhibitory influence exerted by 

 this portion of the hypophysis? This is only a suggestion, and 

 should be regarded as such. 



In this connection it is of paramount importance to know 

 which condition of the chromatophore, the expanded or contracted, 

 is to be regarded as the active or passive phase. If, as assumed 

 by some (Spaeth, '16, and Laurens, '15), the expanded condition 

 of the pigment cell is the passive phase then the persistent expan- 

 sion of the xantholeucophores following hypophysectomy in the 



